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Topic: Fermenter geometry? (Read 6050 times)

I've read that the shape of fermentation vessels has a lot to do with yeast performance, ester production, phenols etc. It would seem to me that a shallow vessel with a larger surface area would grow yeast at a faster rate due to the increased exposure and absorption of oxygen? Would it cause the wort to ferment faster also, and what effect would it produce as far as esters and phenols? Does a shallow vessel produce more either, or does the deeper vessel? Look at the open fermenters used by SN for making Big Foot, considering its volume, it appears shallow with a very large surface area.

I've read that the shape of fermentation vessels has a lot to do with yeast performance, ester production, phenols etc. It would seem to me that a shallow vessel with a larger surface area would grow yeast at a faster rate due to the increased exposure and absorption of oxygen? Would it cause the wort to ferment faster also, and what effect would it produce as far as esters and phenols? Does a shallow vessel produce more either, or does the deeper vessel? Look at the open fermenters used by SN for making Big Foot, considering its volume, it appears shallow with a very large surface area.

I've been wondering about fermenter geometry lately myself. I know for commercial production it can make a big difference but at the homebrew scale I wonder how much impact it would have?

I'm thinking about buying another picnic cooler ( blue )and using it for fermentation.

HamiltonT, I printed that article and read it, are they saying that ale yeast (top cropping) ferments or behaves like lager (bottom cropping) yeast in shallow vessels? If they are I have to wonder if that is necessarily a bad thing or not? Also I noted all the vessels were still cylindrical so I'm not sure what they consider shallow? The article didn't show a value for the diameter of any of the vessels but there was maximum height recommended as I recall. I wish it would have considered other types and designs.

I'm thinking about buying another picnic cooler ( blue )and using it for fermentation.

I have a small one that I could rig up for primary, might try that.

One issue I can think is keeping the temperature down.I would use it for a bitter using 1469 and that throws some heat, coolers are designed to hold in heat/cold. Might get aweful warm in there even in a cool place.

I'd just put a piece of plexiglass on the top with keg lube on the edges to "seal" it. A small hole on one side would allow C02 out.

This was a rather poor paper which gave little detail on the actual results. I’m not even fully clear what the point of the paper was.

The reference to ale yeast acting like lager yeast means that they don’t form as big of a yeast head anymore and collect in the cone rather than in the Kraeusen. I believe that has something to do with the stronger currents in a conical which “wash away” the yeast head.

To my knowledge the most remarkable difference between a conical and an open fermenter is the height. In a conical the yeast experiences a higher hydrostatic pressure which affects the flavor profile of the beer. I remember reading that there was a marked shift in the taste of German beers when most breweries moved to conicals in the 1970s and 1980s. In home brewing there is little increased depth between a conical and an open fermenter but I’m curious if anyone has tried a side-by-side between a conical and a bucket.

BYO had a good article on open fermentation that touched upon fermenter geometry (see link). I am lucky that my first choice for fermentation is my conical, but when that's full and I just have to brew, I will ferment beers in my 15 gallon Polarware kettle which is about 19" diameter x 15" tall. That's pretty close to a 1:1 ratio mentioned in the article, or close enough for me at least. Here's what I've noticed about the kettlementor and some tips:

* 30%-40% faster fermentation in the kettle. In four 10-gallon batches of IPA (two fermented in conical, two in kettle) brewed over the course of three months but with virtually identical recipe/brewing/ferm-temp each time, my 1.064 IPA finished out to 1.014 in 11 days (both times) in the conical versus 5-6 days for both batches fermented in the kettle. I won't bore you with more details, but I've experienced relatively the same thing with Saisons and Hefe's.

* Slight increase in phenol & ester production. It's hard to quantify this, so you'll just have to try. Just choose a beer that benefits from some ester flavor/aroma. You can minimize the esters somewhat by aging the beer in a refridgerator. I have received high scores on beers fermented in my kettle and don't recall ever being "dinged" for too much ester character. Would I ferment a Bohemian Pilsner in a kettle? Probably not. You can do it with lots of ale styles though.

* If your kettlementor has drilled/threaded valves, you might want to clean them out from the inside with a toothbrush prior to a final saniztizing rinse. Those threads collect a lot of gunk.

* I place a 5 lb weight on top of the lid to keep any foreign particles out and hold a decent seal. That does allow for some CO2 seepage. I have also used masking tape around the lid as an added precaution, but I'm not sure it's really necessary. Please note, in a 15 gallon squatty kettlementor, a 10-11 gallon batch is not likely to have krausen up to the lid (at least I never have).

* Because of the wide surface area, the trub is evenly and thinly distributed so I don't get much (if any) running out when I transfer the beer to kegs or secondary. I transfer beer out the spigot, through a tube into the next container. Simple. A few minutes before transferring, I usually put a little half-inch thick piece of wood under the kettle on the spigot side to lift up that side. That encourages the trub to float away from the valve.

Considering all the wierd and wonderful vessels that have been used for fermentation over the years, I don't think it's worth stressing too much over a nicely sanitized covered steel container, whatever it's shape may be. Use good brewing practices, keep everything sanitary, and you'll most likely make great beer!

The question here is if the flavor and fermentation performance differences are a result of the different fermenter geometry (kettle vs. pot) or the “open” fermentation of the pot. Since you are placing a lid on the pot it is not necessarily an open fermentation.

I’m still not convinced that it is the “open” aspect of fermenting in open fermenters that changes the flavor. It can also be a simple fermenter geometry thing and that putting a lid on the open fermenters may give you the same beer. Most “open” fermentation instructions for home brewers still call for placing a lid on the fermenter since only few of us would have an area sanitary and clean enough for truly open fermentation.